|  | 3.4 | Benefits of VLANs
| 3.4.2 | How VLANs help control broadcast activity
Broadcast traffic occurs in every network. Broadcast frequency depends on the types of applications, the types of servers, the amount of logical segmentation, and how these network resources are used. Although applications have been fine-tuned over the past few years to reduce the number of broadcasts they send out, new multimedia applications are being developed that are broadcast and multicast intensive. You need to take preventive measures to ensure against broadcast-related problems. One of the most effective measures is to properly segment the network with protective firewalls that, as much as possible, prevent problems on one segment from damaging other parts of the network. Thus, although one segment may have excessive broadcast conditions, the rest of the network is protected with a firewall commonly provided by a router. Firewall segmentation provides reliability and minimizes the overhead of broadcast traffic, allowing for greater throughput of application traffic. When no routers are placed between the switches, broadcasts (Layer 2 transmissions) are sent to every switched port. This is commonly referred to as a flat network, where there is one broadcast domain across the entire network. The advantage of a flat network is that it can provide both low-latency and high-throughput performance and it is easy to administer. The disadvantage is that it increases vulnerability to broadcast traffic across all switches, ports, backbone links, and users. VLANs are an effective mechanism for extending firewalls from the routers to the switch fabric and protecting the network against potentially dangerous broadcast problems. Additionally, VLANs maintain all the performance benefits of switching. You create firewalls by assigning switch ports or users to specific VLAN groups both within single switches and across multiple connected switches. Broadcast traffic within one VLAN is not transmitted outside the VLAN. Conversely, adjacent ports do not receive any of the broadcast traffic generated from other VLANs. This type of configuration substantially reduces the overall broadcast traffic, frees bandwidth for real user traffic, and lowers the overall vulnerability of the network to broadcast storms. The smaller the VLAN group, the smaller the number of users affected by broadcast traffic activity within the VLAN group. You can also assign VLANs based on the application type and the number of applications broadcasts. You can place users sharing a broadcast-intensive application in the same VLAN group and distribute the application across the campus.